The digestive unit carries the heaviest histology load in any A&P sequence. Every level of the alimentary canal has the same four wall layers (mucosa, submucosa, muscularis externa, serosa) but with diagnostic regional variations. Students who learn to recognize the regional pattern can identify any GI organ from histology alone.
Alimentary canal + accessory organs (Pages 2–3)
Same items + functional roles (Page 4)
Heavy section: GI wall layers + regional variants (Pages 5–6)
Fetal pig / sheep alimentary specimen (Page 7)
Standard six-item check (Page 8)
4 stations (Page 9)
| Canonical answer | Accepted synonyms | Spelling rule / common confusion |
|---|---|---|
| Oral cavity & pharynx | ||
| Tongue | (none) | Skeletal muscle covered by stratified squamous; papillae on dorsal surface |
| Hard palate | (none) | Bony anterior roof of oral cavity |
| Soft palate | (none) | Muscular posterior roof; closes nasopharynx during swallow |
| Uvula | (none) | Posterior projection of soft palate |
| Oropharynx | (none) | Common to digestive + respiratory; covered in respiratory packet |
| Esophagus & stomach | ||
| Esophagus | (none) | Muscular tube; passes through diaphragm at esophageal hiatus |
| Lower esophageal sphincter | Cardiac sphincter, gastroesophageal sphincter | Functional sphincter at gastroesophageal junction |
| Stomach (with regions) | Cardia, fundus, body, pyloric region (any region accepted as canonical when pinned) | Specify region if pinned: cardia (entry), fundus (dome), body (main), pylorus (exit) |
| Greater curvature | (none) | Convex left/inferior border of stomach |
| Lesser curvature | (none) | Concave right/superior border |
| Rugae | (none) | Internal stomach folds visible when stomach is empty |
| Pyloric sphincter | Pylorus | True sphincter; controls gastric emptying into duodenum |
| Small intestine | ||
| Duodenum | (none) | First and shortest segment; receives bile + pancreatic ducts; Brunner’s glands diagnostic |
| Jejunum | (none) | Middle segment; tall plicae circulares with villi; few Peyer patches |
| Ileum | (none) | Final segment; abundant Peyer patches; transitions to large intestine at ileocecal valve |
| Plicae circulares | Circular folds, Kerckring folds | Permanent submucosal folds in small intestine; visible grossly |
| Villi | Villus (singular) | Mucosal projections; small intestine specifically; absent in stomach + large intestine |
| Large intestine | ||
| Cecum | (none) | Pouch at start of large intestine; ileocecal valve at top |
| Vermiform appendix | Appendix | Lymphoid; attached to cecum |
| Ascending colon | (none) | Right side; rises from cecum to right colic flexure |
| Transverse colon | (none) | Crosses abdomen |
| Descending colon | (none) | Left side |
| Sigmoid colon | (none) | S-shaped; transitions to rectum |
| Rectum | (none) | Final straight segment |
| Anal canal | (none) | Terminal segment; transitions from columnar to stratified squamous epithelium |
| Tenia coli | Teniae coli (plural) | Three longitudinal smooth muscle bands on colon; diagnostic for large intestine |
| Haustra | Haustrum (singular) | Pouches in colon wall created by tenia tension |
| Canonical answer | Accepted synonyms | Spelling / common confusion |
|---|---|---|
| Salivary glands | ||
| Parotid gland | (none) | Largest; anterior to ear; serous secretion (purely water + amylase) |
| Submandibular gland | Submaxillary gland | Beneath mandible; mixed serous + mucous (mostly serous) |
| Sublingual gland | (none) | Beneath tongue; mostly mucous |
| Liver | ||
| Liver | (none) | Largest internal organ; right + left lobes externally |
| Right lobe (liver) | (none) | Larger; on right side |
| Left lobe (liver) | (none) | Smaller; crosses midline |
| Caudate lobe | (none) | Posterior; near IVC |
| Quadrate lobe | (none) | Inferior; near gallbladder |
| Falciform ligament | (none) | Separates right and left lobes; remnant of fetal umbilical attachment |
| Hepatic portal vein | Portal vein | Distinguish from hepatic vein → not yet (portal carries nutrient-rich blood TO liver; hepatic carries blood FROM liver) |
| Hepatic artery (proper) | Hepatic artery | Brings oxygenated blood to liver |
| Common hepatic duct | (none) | Drains bile from liver before joining cystic duct |
| Gallbladder & ducts | ||
| Gallbladder | (none) | Pear-shaped sac on visceral liver surface |
| Cystic duct | (none) | Drains gallbladder |
| Common bile duct | CBD | Formed by junction of cystic + common hepatic ducts; opens into duodenum at hepatopancreatic ampulla |
| Pancreas (with ducts) | ||
| Pancreas | (none) | Mixed exocrine + endocrine; specify region if pinned (head, body, tail) |
| Pancreatic duct | Duct of Wirsung | Main duct; joins common bile duct at hepatopancreatic ampulla |
| Hepatopancreatic ampulla | Ampulla of Vater | Junction site; opens into duodenum at major duodenal papilla |
| Sphincter of Oddi | Hepatopancreatic sphincter | Controls flow at duodenal opening |
| GI wall layers (apply to every alimentary section) | ||
| Mucosa | Mucous membrane | Innermost; epithelium + lamina propria + muscularis mucosae |
| Submucosa | (none) | Connective tissue with vessels, nerves (Meissner’s plexus), glands |
| Muscularis externa | Muscularis propria | Inner circular + outer longitudinal smooth muscle (3 layers in stomach); Auerbach’s (myenteric) plexus between |
| Serosa (or adventitia) | Visceral peritoneum (when serosa) | Outermost; serosa = mesothelium + connective tissue (most of GI); adventitia = connective tissue only (esophagus, anal canal, retroperitoneal segments) |
| Structure | Acceptable function statement | What does NOT pass |
|---|---|---|
| Tongue | Mechanical mixing and propulsion of food bolus; taste reception via papillae; speech articulation | "Tastes" alone |
| Esophagus | Conducts food bolus from pharynx to stomach via peristalsis; no digestion or absorption | "Carries food" alone |
| Stomach | Mechanical churning + chemical digestion (HCl + pepsin) producing chyme; some absorption (alcohol, aspirin) | "Digests food" alone |
| Pyloric sphincter | Controls rate of gastric emptying into duodenum; prevents reflux | "Closes" alone |
| Duodenum | First site of major chemical digestion (bile + pancreatic enzymes enter here); neutralizes gastric acid | "Small intestine" alone |
| Jejunum | Primary site of nutrient absorption; tall villi maximize surface area | "Absorbs" alone (must indicate primary site) |
| Ileum | Absorbs vitamin B12 + bile salts; immune surveillance via Peyer patches | "Absorbs nutrients" alone (must indicate B12 / bile salts) |
| Large intestine (colon) | Absorbs water and electrolytes; compacts feces; bacterial fermentation produces vitamin K + some B vitamins | "Stores waste" alone (must indicate absorption) |
| Liver (general) | Bile production; metabolic processing of nutrients from portal blood; detoxification; protein synthesis (albumin, clotting factors); glycogen storage | "Filters blood" alone |
| Gallbladder | Stores and concentrates bile produced by liver; releases bile in response to CCK from duodenum | "Holds bile" alone |
| Pancreas (exocrine) | Produces digestive enzymes (amylase, lipase, proteases as zymogens) + bicarbonate-rich fluid for duodenum | "Makes enzymes" alone |
| Salivary glands | Produce saliva containing amylase (starch digestion), lysozyme (antimicrobial), mucus (lubrication) | "Make saliva" alone (must indicate component function) |
| Mucosa | Innermost layer providing barrier + secretion + absorption; epithelium varies by region (stratified squamous in esophagus and anal canal; simple columnar elsewhere) | "Lining" alone |
| Muscularis externa | Smooth muscle producing peristalsis (waves of contraction propelling content distally) + segmentation (mixing) | "Moves food" alone (must indicate peristalsis / segmentation) |
| Slide | Canonical identification | Two features required |
|---|---|---|
| Esophagus | Esophagus | Stratified squamous epithelium (key vs all post-esophagus segments) · Submucosal mucous glands (esophageal glands proper) · Muscularis: skeletal muscle (proximal), mixed (middle), smooth muscle (distal) · Adventitia (no serosa above diaphragm) |
| Stomach | Stomach | Gastric pits with simple columnar surface mucous cells · Gastric glands containing parietal cells (large pink, HCl) and chief cells (basophilic, pepsinogen) · Three muscle layers in muscularis externa (oblique + circular + longitudinal) · No villi |
| Duodenum | Duodenum | Villi (small intestine signal) · Brunner’s glands in submucosa (DUODENUM-specific, mucous glands buffering acid chyme) · Plicae circulares · Simple columnar with goblet cells |
| Jejunum | Jejunum | Tallest, most prominent villi · Plicae circulares prominent · Few or no Peyer patches · Goblet cells throughout · Crypts of Lieberkühn at villus base |
| Ileum | Ileum | Peyer patches (large lymphoid aggregates in submucosa, sometimes extending into mucosa, DIAGNOSTIC) · Shorter villi than jejunum · More goblet cells · Plicae circulares less prominent |
| Large intestine (colon) | Large intestine | NO villi (key feature) · Numerous goblet cells in straight crypts · Tenia coli visible (longitudinal muscle in three bands) · Simple columnar with absorptive cells + abundant goblet cells |
| Slide | Canonical identification | Two features required |
|---|---|---|
| Liver | Liver | Hepatic lobules (hexagonal arrangements with central vein) · Hepatocytes in radiating cords from central vein · Sinusoids between cords (lined by Kupffer cells) · Portal triad at lobule corners (hepatic artery branch + portal vein branch + bile duct) |
| Gallbladder | Gallbladder | Simple columnar epithelium with prominent microvilli · Mucosal folds (rugae) when relaxed · No submucosa as a distinct layer (uniquely thin) · Smooth muscle layer · Outer adventitia (or serosa where applicable) |
| Pancreas | Pancreas | Exocrine acini (densely packed, basophilic cells with apical zymogen granules) · Endocrine islets of Langerhans (pale rounded clusters among acini) · Intralobular ducts with cuboidal epithelium · Centroacinar cells extending into acini (DIAGNOSTIC for pancreas) |
| Submandibular gland | Submandibular gland (mixed) | Mostly serous acini with darker basophilic cells + apical secretory granules · Some mucous acini with paler vacuolated cells · Serous demilunes capping mucous acini · Striated ducts |
For any GI tract slide, identify the four layers from lumen outward: mucosa (epithelium + lamina propria + muscularis mucosae), submucosa (connective tissue + vessels + nerves + sometimes glands), muscularis externa (inner circular + outer longitudinal smooth muscle, plus oblique in stomach), and serosa or adventitia (mesothelium + connective tissue, or connective tissue alone). Naming all four passes R3 even if regional identification is partial.
Most A&P programs use either fetal pig (for whole alimentary canal in continuity) or sheep stomach + small intestine specimens. The R4 rubric is the same regardless of specimen choice; the observable criteria below apply to either.
Whole-pig and intact intestinal preparations are time-intensive to prepare. A student who damages the alimentary continuity (cuts through small intestine and discards a section, etc.) impacts cohort access for the rest of the term. The repeat-on-second-specimen rule is one per student per term for that reason; further attempts require coordinator consultation.
Digestive is the unit that drills the four-layer framework. By the end of the unit, students who have labeled all four layers on every sketch can identify any GI tract section in the capstone with confidence; students who skip the labeling typically struggle with region differentiation later. The notebook discipline forces the framework to stick.
The digestive unit contributes 4 stations to the term-end capstone (heavier weight reflecting the unit’s histology load). Each is 90 seconds; passes at 3 of 4; excellence at 4 of 4.
ID structure. Function. Clinical: one pathology (GERD, gastric ulcer, IBS, diverticulitis). Integration: relate to enteric nervous system or autonomic control.
ID organ. Function. Clinical: one pathology (cholecystitis, pancreatitis, hepatitis, cirrhosis). Integration: relate to a different system (endocrine via insulin from pancreas, blood via hepatic protein synthesis).
ID GI region from histology alone (must name the segment, not just “small intestine”). Function. Clinical: one diagnostic finding visible in disease state. Integration: relate to neighboring segments by functional sequence.
ID accessory organ from histology. Function. Clinical: one disease association. Integration: relate to alimentary canal segment it serves.
| Outcome per station | Counted as |
|---|---|
| 4 / 4 | Excellence (counts toward A bundle) |
| 3 / 4 | Pass (counts toward B and C bundles) |
| ≤ 2 / 4 | Not yet (counts toward D bundle if attempted; no F-bundle credit) |
| No attempt | Not counted toward any bundle |
Student: ______________________________________ Section: _______________ Date: _______________ TA: _______________
| # | Item | ID (R1) | Function (R2) |
|---|---|---|---|
| 1 | Stomach region (cardia / fundus / body / pylorus) | P / NY | P / NY / — |
| 2 | Small intestine segment | P / NY | P / NY / — |
| 3 | Large intestine segment | P / NY | P / NY / — |
| 4 | Sphincter identification | P / NY | P / NY / — |
| 5 | Liver lobe / structure | P / NY | P / NY / — |
| 6 | Gallbladder + duct system | P / NY | P / NY / — |
| 7 | Pancreas (gross) | P / NY | P / NY / — |
| 8 | Salivary gland | P / NY | P / NY / — |
| # | Slide | ID | ≥2 features | All 4 wall layers labeled |
|---|---|---|---|---|
| 9 | GI tract section (region ID required) | P / NY | P / NY | P / NY |
| 10 | Liver | P / NY | P / NY | — |
| 11 | Pancreas | P / NY | P / NY | — |
| Item | Criterion | Met |
|---|---|---|
| D1 | Pre-dissection inspection | P / NY |
| D2 | Tools used appropriately | P / NY |
| D3 | Alimentary continuity preserved | P / NY |
| D4 | Accessory organs identified in situ | P / NY |
| D5 | Cleanup and storage | P / NY |
| R4 | Overall (5 of 5 = pass) | P / NY |
☐ No ☐ Yes — for item: __________ Tokens remaining: ☐ 3 ☐ 2 ☐ 1 ☐ 0